Animals Live Longer When They Don’t Reproduce

Reproduction has long been viewed as a biological imperative, but a new international study suggests it may also come with a hidden cost: a shorter life. Research published Wednesday in the journal Nature reports that sterilization and hormonal contraception are associated with increased lifespan across a wide range of vertebrate animals, reinforcing long-standing evolutionary theories about the trade-offs between reproduction and longevity.

The study, titled “Sterilization and contraception increase lifespan across vertebrates,” was published on December 10, 2025, and led by Michael Garratt, an associate professor at the University of Otago in New Zealand. The research involved a large international team including Malgorzata Lagisz, Johanna Staerk, Christine Neyt, and other collaborators from institutions in Europe, North America, and Australasia.

Using data from zoo and aquarium populations worldwide, the researchers analyzed lifespan records from more than 100 vertebrate species, with a primary focus on mammals. These records were compared across individuals that had undergone reproductive interventions — such as surgical sterilization or long-term hormonal contraception — and those that had not.

Across species, animals whose reproduction was suppressed consistently lived longer than their reproductively intact counterparts, the study found.

“Our results provide some of the strongest comparative evidence to date that reproduction itself carries measurable survival costs,” Garratt said. “When reproduction is reduced or prevented, resources that would otherwise go toward producing offspring can instead be invested in maintaining the body.”

The findings align with a core concept in evolutionary biology known as the life-history trade-off, which holds that organisms have finite energy to allocate between growth, reproduction, and survival. Investing heavily in one often limits the others.

Differences Between the Sexes

One of the study’s key findings is that the longevity benefit of suppressing reproduction differs between males and females.

In males, increased lifespan was primarily associated with castration, especially when it occurred before puberty. Vasectomy alone — which prevents reproduction without significantly altering hormone levels — did not show the same effect. This suggests that sex hormones such as testosterone play a central role in shaping aging and mortality risk.

“Testosterone influences behavior, metabolism, and immune function,” Garratt said. “Reducing its influence early in life appears to have long-term consequences for survival.”

In females, the picture was more complex. Both surgical sterilization and hormonal contraception were linked to longer lifespan, though the magnitude of the benefit varied by species. Researchers suggest that pregnancy, lactation, and repeated reproductive cycles impose substantial physiological demands that can accelerate aging over time.

A Broader Biological Perspective

Co-author Malgorzata Lagisz, an evolutionary biologist, emphasized that the study goes beyond individual species and points to a deeply conserved biological pattern.

“What is striking is how consistent this relationship is across very different vertebrates,” Lagisz said. “Despite differences in ecology, body size, and lifespan, the cost of reproduction shows up again and again.”

Lagisz noted that the research also included a meta-analysis of previous experimental and observational studies, encompassing rodents, laboratory animals, and wildlife populations. The consistency of the findings, she said, strengthens confidence that the effect is not limited to captive animals alone.

Still, both researchers cautioned against oversimplifying the implications.

“This is not a recommendation,” Lagisz said. “Reproduction is essential at the population level, even if it carries costs at the individual level.”

Although the study includes some observational data from humans, the authors stress that human longevity is shaped by many additional factors, including healthcare, nutrition, social conditions, and lifestyle.

“Humans are not just biological organisms — we live in complex societies,” Garratt said. “That makes direct comparisons difficult.”

Previous historical data, such as records of castrated men in specific cultural contexts, have suggested similar longevity patterns, but the authors emphasize that such evidence remains limited and ethically sensitive.

Vertebrate Diversity

The study’s conclusions extend across the vertebrate lineage, a group that includes mammals, birds, reptiles, amphibians, and fish — all animals united by the presence of a backbone.

While mammals formed the bulk of the dataset, the broader analysis suggests that the reproduction–longevity trade-off may be a fundamental feature of vertebrate biology, regardless of whether an animal gives birth to live young, lays eggs, or reproduces externally.

From long-lived parrots and tortoises to short-lived rodents and fish, the findings indicate that how an organism allocates energy between reproduction and self-maintenance is a key determinant of lifespan.

As researchers continue to explore aging across the tree of life, this study underscores a provocative idea, for vertebrates, living longer may often mean reproducing less — a biological trade-off written deep into evolution itself. (Sulung Prasetyo)